Boom inclination detecting and stabilizing system

ABSTRACT

Apparatuses and methods for controlling the stability of elevating systems, such as personnel lifts. In one embodiment, a stability control apparatus includes an angle detector and a signal processor. The angle detector is mounted to a boom of a personnel lift and configured to detect an angle of inclination of the boom relative to an independent reference frame independent of the personnel lift. The signal processor is operatively connected to the angle detector and is configured to receive a first signal initiated by the angle detector when the angle of inclination reaches a predetermined angle. The signal processor is further configured to output a second signal in response to receiving the first signal causing a boom control system to limit movement of the boom relative to the independent reference frame when the angle of inclination reaches the predetermined angle.

TECHNICAL FIELD

[0001] The present invention is directed to apparatuses and methods for controlling the stability of elevating systems and, more particularly, to apparatuses and methods for controlling the stability of personnel lifts by detecting angles of boom inclination.

BACKGROUND

[0002] Personnel lifts and other elevating systems are widely used to provide persons, machines, and materials with temporary access to elevated or otherwise inaccessible work areas. Typical personnel lifts include a work platform mounted to a distal end of an extendible boom or other type of lift assembly. A proximal end of the extendible boom is often pivotally connected to a base or other structure so that the boom can pivot in a vertical plane relative to the base to vertically position the work platform. In addition, the base is often rotatably mounted to a chassis so that the base can rotate in a horizontal plane relative to the chassis to horizontally position the work platform. Such rotatable bases are commonly referred to as “turntables.” The pivoting boom and rotating base enable the personnel lift to reach a wide range of elevated locations without having to reposition the chassis. However, many personnel lift chassis are equipped with wheel-sets to facilitate repositioning of the personnel lifts when desired. Examples include both self-propelled and trailerable personnel lifts.

[0003]FIGS. 1A and 1B are side elevational views of a conventional personnel lift 100 in accordance with the prior art. As shown in FIG. 1A, the prior art personnel lift 100 includes an extendible boom 101 pivotally connected to a chassis 104 at a proximal end 103. A work platform 106 is supported by the boom 101 at a distal end 105. In operation, the boom 101 can pivot about the proximal end 103 relative to the chassis 104 to position an operator (not shown) in the work platform 106 at a desired elevation.

[0004] With many prior art personnel lifts, as the boom 101 is pivoted upwardly, its rotational speed increases. This increase in rotational speed can be attributed to a number of factors related to a boom angle A between the boom 101 and the chassis 104. One such factor is a decrease in load-moment: As the boom angle A increases, the load-moment acting on the boom decreases, thereby making it progressively easier for the boom lift mechanism (typically a hydraulic cylinder) to lift the boom. Another such factor is an increase in lifting force: Increasing the boom angle A can improve the geometric relationship between the lift mechanism and the boom, thereby increasing the lifting force applied to the boom.

[0005] The increased rotational speed of the boom 101 as it nears the top of its arc can impart considerable rotational inertia to the boom. As a result, if the boom 101 is stopped abruptly near the top of its arc this rotational inertia can cause the personnel lift 100 to experience a jolt in the direction of boom rotation that is resisted by the chassis 104. On level ground, such as that shown in FIG. 1A, this jolt may not be sufficient to destabilize the personnel lift 100. However, if the chassis 104 is positioned on a sloped surface, such as that shown in FIG. 1B, then this jolt could be sufficient to reduce the stability of the personnel lift 100.

SUMMARY

[0006] The present invention is directed toward apparatuses and methods for controlling the stability of elevating systems, such as personnel lifts. In one embodiment of the invention, a stability control apparatus is usable with an elevating system having a boom operatively connected to a chassis and a control system operatively connected to the boom for controlling movement of the boom relative to the chassis. In one aspect of this embodiment, the stability control apparatus includes an angle detector and a signal processor. The angle detector is adapted to be operatively mounted to the elevating system and is configured to detect an angle of inclination between a portion of the elevating system and an independent reference frame independent of the chassis. The signal processor is operatively connected to the angle detector and is configured to receive a first signal initiated by the angle detector and output a second signal in response to receiving the first signal; the second signal causing the control system to limit or otherwise modify movement of the boom relative to the independent reference frame.

[0007] In another embodiment of the invention, a method for moving a boom from a first position to a second position is usable with a boom operatively connected to a chassis and a control system, the control system controlling movement of the boom relative to the chassis. In one aspect of this embodiment, the method includes detecting a boom angle relative to an independent reference frame independent of the chassis, and allowing pivotal movement of the boom relative to the independent reference frame when the boom angle relative to the independent reference frame is within a first range of angles. The method further includes limiting pivotal movement of the boom relative to the independent reference frame when the boom angle relative to the independent reference frame is within a second range of angles, the second range of angles including steeper angles of inclination than the first range of angles.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIGS. 1A and 1B are side elevational views of a conventional personnel lift in accordance with the prior art.

[0009]FIG. 2 is a partial schematic isometric view of a personnel lift having a stability control apparatus in accordance with an embodiment of the invention.

[0010]FIG. 3 is an enlarged partial schematic side elevational view of the stability control apparatus of FIG. 2 taken substantially along line 3-3 in FIG. 2 in accordance with an embodiment of the invention.

[0011]FIG. 4 is a graph illustrating a plot of boom speed verses boom angle relative to an independent reference frame, provided by a method of boom control in accordance with an embodiment of the invention.

[0012]FIG. 5 is a side elevational view of the personnel lift of FIG. 2 taken substantially along line 5-5 in FIG. 2 illustrating various boom positions relating to the graph of FIG. 4 in accordance with an embodiment of the invention.

[0013]FIG. 6 is an isometric view of a personnel lift having a stability control apparatus in accordance with another embodiment of the invention.

DETAILED DESCRIPTION

[0014] The following disclosure describes apparatuses and methods for controlling the stability of elevating systems, such as personnel lifts. Certain specific details are set forth in the following description and in FIGS. 2 through 6 to provide a thorough understanding of various embodiments of the invention. Those of skill in the relevant art will understand, however, that the present invention may have additional embodiments, or that the invention may be practiced without several of the details described below. In other instances, well-known structures associated with personnel lifts, such as extendible booms, hydraulic control systems and the like, have not been shown or described in detail here to avoid unnecessarily obscuring the description of the embodiments of the invention.

[0015]FIG. 2 is a partial schematic isometric view of a personnel lift 200 having a stability control apparatus 210 in accordance with an embodiment of the invention. In the illustrated embodiment, the personnel lift 200 includes a primary boom 201 pivotally connected to a secondary boom 202 at a proximal end 203 of the primary boom. A lift mechanism 212 (e.g., a lift cylinder) provides the force that pivots the primary boom 201 upwardly and downwardly relative to the secondary boom 202. The primary boom 201 supports a platform 206 at a distal end 205 of the primary boom. The secondary boom 202 is pivotally connected to a base 220, which in turn is rotatably mounted to a chassis 204. The rotatable base 220 of the illustrated embodiment is commonly referred to as a “turntable.” Accordingly, the base 220 will be referred to in the following disclosure as the “turntable” 220. The chassis 204 is a self-propelled and stearable “drive chassis” that includes a forward wheel-set 208 and a rear wheel-set 209.

[0016] Platform controls 231 (e.g., one or more joysticks, levers, switches and the like) are mounted on the platform 206 to enable an operator on the platform (not shown) to control movement of the personnel lift 200. In addition, similar ground controls 232 are mounted on the turntable 220 to enable an operator on the ground (also not shown) to control movement of the personnel lift 200. Such movements of the personnel lift 200 can include pivotal articulation and extension/retraction of the primary boom 201 and the secondary boom 202 relative to the turntable 220, rotational motion of the turntable relative to the drive chassis 204, and rolling motion of the drive chassis relative to the ground. As illustrated in FIG. 2, both of the operator controls (i.e., the platform controls 231 and the ground controls 232) are operatively connected to a personnel lift control system 230 (shown schematically) contained within the turntable 220 and operatively connected to the systems providing motive power to the personnel lift 200 (such as an internal combustion engine and/or a boom hydraulic system). The control system 230 receives operator control inputs via the operator controls and controls movement of the personnel lift 200 (i.e., the primary boom 201, the secondary boom 202, the turntable 220, and/or the drive chassis 204) in response to the operator control inputs.

[0017] In one aspect of this embodiment, the stability control apparatus 210 includes an angle detector 240 mounted toward the proximal end 203 of the primary boom 201. As will be explained in greater detail below, the angle detector 240 is configured to detect an angle of inclination 244 of the primary boom 201. The angle of inclination 244 is defined, for purposes of this disclosure, to be the angle formed between a longitudinal axis 246 of the primary boom 201 and an independent reference frame 241. The independent reference frame 241 of the illustrated embodiment is represented by a horizontal line positioned normal to the direction of gravitational force. Accordingly, the independent reference frame 241 is independent of the position or orientation of the chassis 204 or other components of the personnel lift 200.

[0018] In a further aspect of this embodiment, the angle detector 240 is operatively connected to a processor 242 (shown schematically), and is configured to send the processor a first signal related to the detected angle of inclination 244. In one embodiment, the first signal can be an analog signal such as a voltage signal that is proportional to the gravitational acceleration acting on the angle detector 240. In other embodiments, the first signal can be other types of signals indicative of the angle of inclination 244. The processor 242 may be contained in the turntable 220 and is operatively connected to the control system 230. The processor 242 is configured to send the control system 230 a second signal related to the first signal in response to receiving the first signal from the angle detector 240. As will be explained in greater detail below, in one embodiment, the second signal can be a digital signal configured to cause the control system 230 to limit movement of the personnel lift 200 based on the detected angle of inclination 244.

[0019] During transport or periods of nonuse of the personnel lift 200, the primary and secondary booms 201 and 202 can be retracted and collapsed into a stowed configuration (not shown). When use is desired, persons and/or materials can be loaded onto the platform 206 and an operator, positioned at either the platform controls 231 or the ground controls 232, can position the platform 206 at a desired elevation by controlling the angle and/or extension of one or both of the primary and secondary booms 201 and 202 relative to the chassis 204. As the primary boom 201 pivots in a direction 250, the angle detector 240 detects the increasing angle of inclination and sends a signal to the processor 242 relating to the angle of inclination. When the angle of inclination 244 reaches a predetermined angle (such as an upper operational limit of boom rotation), the processor 242 sends a signal to the control system 230 causing the control system 230 to limit movement of the personnel lift 200. In one embodiment, the control system 230 limits movement of the primary and secondary booms 201 and 202 and/or movement of the drive chassis 204 to only those movements which tend to maintain or increase the stability of the personnel lift. In one aspect of this embodiment, such limited movements can include 1) gradually reducing the rotational speed of the primary boom 201 in the direction 250 to slowly dissipate the rotational inertia of the primary boom, 2) stopping rotation of the primary boom in the direction 250 at the upper operational limit of boom rotation, and 3) disabling the drive chassis 204 to prevent repositioning of the drive chassis on unfavorably inclined surfaces.

[0020] As will be apparent to those of ordinary skill in the art, one advantage of the personnel lift 200 of the present invention is that the angle of inclination 244 is detected by the angle detector 240 irrespective of the position or orientation of the chassis 204. As a result, positioning the drive chassis 204 on an inclined surface will not compromise the ability of the stability control apparatus 210 to detect a potentially unstable boom position. These and other aspects of the stability control apparatus 210 will be described in greater detail below in reference to the Figures that follow.

[0021]FIG. 3 is an enlarged partial schematic side elevational view of the stability control apparatus 210 taken substantially along line 3-3 in FIG. 2 in accordance with an embodiment of the invention. In one aspect of this embodiment, the angle detector 240 is a uniaxial accelerometer or other instrument capable of measuring axial accelerations along a functional axis 342. In the illustrated embodiment, the angle detector 240 is fixedly mounted toward the proximal end 203 of the primary boom 201 in functional alignment with the longitudinal axis 246 of the primary boom. In other embodiments, the angle detector 240 can be mounted to the primary boom 201 at different locations on the primary boom. However, regardless of the mounting location of the angle detector on the primary boom, in accordance with one aspect of the invention, the functional axis 342 of the angle detector 240 should be at least approximately parallel to the longitudinal axis 246 of the primary boom 201.

[0022] As shown in FIG. 3, the angle detector 240 is operatively coupled to the processor 242 via an electrical link 352, such as an electrical cable. Although not shown in FIG. 3, in one aspect of this embodiment, the electrical link 352 is routed along the primary boom 201 and the secondary boom 202 to the processor 242 in the turntable 220 in such a way as to prevent the electrical link from sustaining damage during boom operation.

[0023] In operation, the angle detector 240 measures the component of gravitational acceleration acting parallel to the longitudinal axis 246 as a function of the angle of inclination 244 of the primary boom 201. For example, when the primary boom 201 is positioned with its longitudinal axis 246 substantially parallel to the horizontal line 241, as shown by the solid lines in FIG. 3, the angle detector 240 measures a gravitational acceleration along its functional axis 342 of zero. In contrast, when the primary boom 201 is pivoted into a more vertical position, as shown by the dotted lines in FIG. 3, the angle detector 240 measures a gravitational acceleration along its functional axis 342 approaching one G (i.e., the gravitational constant G of 32.2 ft/sec²). Accordingly, as the primary boom 201 pivots through its arcuate range of motion, the angle detector 240 measures gravitational accelerations ranging from zero to about one G, and sends a signal corresponding to the measured accelerations to the processor 242.

[0024] In one aspect of this embodiment, the processor 242 is configured to convert the measured gravitational accelerations into corresponding angles of inclination 244 of the primary boom 201. For example, a measured gravitational acceleration of zero Gs would correspond to an angle of inclination 244 of zero degrees and, accordingly, a measured acceleration of one G would correspond to an angle of inclination of 90 degrees. In a further aspect of this embodiment, essentially any angle of inclination 244 can be found by using equation 1 below: $\begin{matrix} {{{Angle}\quad {of}\quad {inclination}} = {{Sin}^{- 1}\left( \frac{{Measured}\quad {Accel}}{G} \right)}} & (1) \end{matrix}$

[0025] Thus, for example, if the angle detector 240 measures a gravitational acceleration of 0.707Gs, then the corresponding angle of inclination 244 would be equal to 45 degrees.

[0026] In a further aspect of this embodiment, once the processor 242 has converted the gravitational acceleration measurement from the angle detector 240 into a corresponding angle of inclination 244, the processor sends a corresponding signal to the control system 230 (not shown). As will be explained in greater detail below with reference to FIGS. 4 and 5, the control system 230 can utilize the second signal from the processor 242 to control the stability of the personnel lift 200 (FIG. 2) by controlling movement of the primary boom 201, the secondary boom 202, and/or the drive chassis 204.

[0027] Although the angle detector 240 illustrated in FIG. 3 in one embodiment is an accelerometer, those of ordinary skill in the relevant art will recognize that the angle detector 240 can be other types of angle detectors without departing from the spirit or scope of the present disclosure. For example, in one such alternate embodiment, the angle detector 240 can be a pendulum switch. Rather than measuring gravitational accelerations, a pendulum switch measures angle of inclination using a pendulum-type member operatively connected to a measuring device to measure the angle between the pendulum-type member and, for example, the longitudinal axis 246 of the primary boom 201. This angle can then be used to determine the angle of inclination 244 of the primary boom 201. In other embodiments, other types of angle detectors can be utilized consistent with this disclosure as necessary to suit the particular application.

[0028]FIG. 4 illustrates a graph 400 showing boom speed verses boom angle provided by one method of boom control in accordance with an embodiment of the invention. In one aspect of this embodiment, boom speed is measured along a vertical axis 402 in inches per second and boom angle is measured along a horizontal axis 404 in degrees. The term “boom speed,” for purposes of this discussion, refers to the speed of the primary boom 201 at the distal end 205 (FIG. 2). Accordingly, “boom speed” is proportional to the rotational speed of the primary boom 201 and the length of the primary boom. The term “boom angle,” for purposes of this discussion, refers to the angle of inclination 244 (FIGS. 2 and 3).

[0029] As discussed above with reference to FIG. 2, a common characteristic of personnel lifts utilizing extendible booms is that the rotational speed of the primary boom 201 increases as the angle of inclination 244 approaches the vertical position. As explained above, this increasing rotational speed can be due to a number of factors including, for example, the reduction in load-moment acting on the boom lift mechanism as well as the more favorable geometric relationship that may exist between the lift mechanism and the primary boom 201 as the primary boom approaches the vertical position. A plot 406 on the graph 400 corresponds to the maximum normal operating speed of the primary boom 201 (FIG. 2) and illustrates the increase in rotational speed of the primary boom as the boom angle increases. As can be seen, when the lifting force on the primary boom 201 from the lifting mechanism 212 (FIG. 2) remains constant, the boom speed is relatively low at low boom angles and gradually increases as the boom angle increases. For example, at zero degrees (i.e., where the primary boom 201 is horizontal) the boom speed is approximately 10-15 inches per second, while at 70 degrees the boom speed is approximately 40 inches per second. As explained above, a high boom speed may have unfavorable consequences at high angles of inclination because the rotational inertia of the primary boom 201 may cause the personnel lift 200 (FIG. 2) to experience a jolt in the direction of rotation when the boom motion is stopped. This jolt may not be problematic when the chassis 204 is positioned on a relatively horizontal surface. However, if the chassis is maneuvered onto an inclined surface, this jolt could reduce the stability of the personnel lift 200.

[0030] In recognition of this problem, one aspect of an embodiment of the present invention is to limit the boom speed of the primary boom 201 as the primary boom approaches a vertical position. Accordingly, a plot 408 on the graph 400 illustrates one method for controlling boom speed in accordance with this embodiment. As can be seen with reference to the plot 408, this method entails gradually reducing the boom speed between about 35 degrees and 65 degrees, substantially reducing boom speed between about 65 degrees and 70 degrees, and preventing boom rotation beyond 73 degrees. In one embodiment, boom speed can be reduced via the control system 230 by reducing the lifting force applied by the lift mechanism 212 (FIG. 2). As will be understood by those of ordinary skill in the relevant art, the plot 408 represents only one of many possible methods for controlling boom speed in accordance with this disclosure. In other embodiments, other methods of boom control can be implemented to suit the particular applications. The plot 408 will be further described in conjunction with the description of FIG. 5 that follows.

[0031]FIG. 5 is a side elevational view of the personnel lift 200 of FIG. 2 taken substantially along line 5-5 in FIG. 2 for the purpose of describing the method of boom control illustrated in FIG. 4 in accordance with an embodiment of the invention. In one aspect of the illustrated embodiment, the primary boom 201 has a total range of motion relative to the independent reference frame 241 between a first boom position 501 and a sixth boom position 506. However, the operational range of motion of the primary boom 201 is between the first boom position 501 and a fourth boom position 504. In a further aspect of this embodiment, the first boom position 501 is a mechanical stop determined by the lift mechanism configuration and is about 35 degrees below the independent reference frame 241. In yet another aspect of this embodiment, the fourth boom position 504 is about 68 degrees above the independent reference frame 241. In other embodiments, the first and forth boom positions 501 and 504 can be other angles.

[0032] As the primary boom 201 sweeps through its arc between the first boom position 501 and the fourth boom position 504, the angle detector 240 measures the corresponding angle of inclination 244 relative to the independent reference frame 241 (i.e., relative to a horizontal line normal to the direction of gravitational force). The angle of inclination 244 measured by the angle detector 240 is sent to the control system 230 via the processor 242 (FIG. 2). In one aspect of this embodiment, the control system 230 controls movement of the primary boom 201 in accordance with the plot 408 shown in FIG. 4 based on the angle of inclination 244 received from the processor 242. In an alternate embodiment, the processor 242 can be utilized to determine the rotational velocity of the primary boom 201 by determining the rate of change of the angle of inclination of the primary boom 201 (i.e., the first derivative of the angle). In this alternate embodiment, the control system 230 controls movement of the primary boom 201 based on the rotational velocity of the primary boom received from the processor 242.

[0033] Referring to FIGS. 4 and 5 together, in the illustrated embodiment, the primary boom 201 is free to move between the range of angles including the first boom position 501 and a second boom position 502 substantially without any imposed constraints on motion. In one aspect of this embodiment, the angle detector 240 becomes active at the second boom position 502. In a further aspect of this embodiment, the second boom position 502 can be between about 30 degrees and about 90 degrees above the independent reference frame 241. In the illustrated embodiment, for example, the second boom position 502 is approximately 33 degrees above the independent reference frame 241. In other embodiments, the second boom position 502 can be other angles.

[0034] As shown in FIG. 4, at the second boom position 502, if the primary boom 201 is travelling at or near its maximum normal operating speed (as indicated by the plot 406), the control system 230 (not shown) begins to limit or reduce the maximum speed of the primary boom 201 based on the signal initiated from the angle detector 240 as the primary boom continues to pivot upwardly through the range of angles including a third boom position 503. At the third boom position 503, the control system 230 slows the primary boom 201 even further until the primary boom reaches the fourth boom position 504 (i.e., the upper operational limit). In one aspect of this embodiment, the third boom position 503 can be between about 60 degrees and about 80 degrees above the independent reference frame 241. In the illustrated embodiment, for example, the third boom position 503 is about 65 degrees. In a further aspect of this embodiment, the fourth boom position 504 can be between about 60 degrees and 90 degrees above the independent reference frame 241. In the illustrated embodiment, for example, the fourth boom position 504 is about 68 degrees. In other embodiments, other angles can be used.

[0035] In another aspect of this embodiment, the control system 230 prevents the lift mechanism 212 (FIG. 2) from pivoting the primary boom 201 any further upwardly when the primary boom is at the upper operational limit of about 68 degrees corresponding to the fourth boom position 504. Thus, further motion of the primary boom 201 upwardly relative to the chassis 204 from this position is no longer possible using the boom lift mechanism 212. However, the control system 230 is configured to permit downwardly movement of the primary boom 201 away from the fourth boom 504 toward shallower angles of inclination. In addition, an audible alarm sounds at both the ground controls 232 and the platform controls 231. Such an audible alarm can include a loud beep or a series of beeps at a preset rate. In a further aspect of this embodiment, a number of visual alarms or indicators can also be implemented at the ground controls 232 and/or the platform controls 231. For example, the platform controls 231 can include a flashing “boom down” light indicating to the operator (not shown) that the boom should be lowered. Similarly, the ground controls 232 could include a flashing “lower boom” light with similar import. In yet another aspect of this embodiment, the foregoing audible/visual alarms can be configured to flash and sound as long as one or more of the boom controls, such as a joystick, is held in an “up boom” position.

[0036] Should the primary boom 201 move past the fourth boom position 504 and approach a fifth boom position 505, for example, by driving the chassis 204 onto a slope that increases the angle of inclination 244, the audible and/or visual alarms shall continue to flash and sound in more amplified modes to notify the operator that the personnel lift 200 may be in, or approaching, an unstable condition. In one aspect of this embodiment, the fifth boom position 505 can be between about 65 degrees and about 90 degrees above the independent reference frame 241. In the illustrated embodiment, for example, the fifth boom position 505 is about 70 degrees. In other embodiments, the fifth boom position 505 can be other angles steeper than the fourth boom position 504 (i.e., the upper operational limit). In another aspect of this embodiment, when the primary boom 201 is in the fifth boom position 505, the drive chassis 204 is disabled so that it cannot continue to propel the personnel lift 200. At this point, to continue operation, the operator must lower the primary boom 201. Accordingly, this is the only boom movement allowed by the control system 230 (FIG. 2). When the primary boom 201 is lowered to within the operational range (i.e., between boom positions 501 and 504) all of the alarms are deactivated and the drive chassis 204 is again enabled, allowing the operator to reposition the personnel lift 200.

[0037] If, however, the primary boom 201 somehow reaches a sixth boom position 506, the control system 230 will shut down or otherwise disable the main power systems on the personnel lift 200 (such as a boom hydraulic system and the ignition and fuel solenoid for a diesel engine housed within the turntable 220). In addition, all audible and/or visual alarms will continue to sound and flash in the amplified modes. In this situation, the only way to lower the primary boom 201 to a more stable configuration is to utilize an auxiliary power system (e.g., an auxiliary hydraulic system driven by an electric motor) to bleed down the boom lift mechanism and lower the boom. Such an auxiliary power system can be started and operated by an operator located either on the ground or on the personnel lift platform. Once the boom has been lowered to within the operable range (i.e., at or below the fourth boom position 504), the main power systems can be restarted and normal use can resume. In one aspect of this embodiment, the sixth boom position 506 can be between about 65 degrees and about 90 degrees above the independent reference frame 241. In the illustrated embodiment, for example, the sixth boom position 506 is about 73 degrees. In other embodiments, the sixth boom position 506 can be other angles steeper than the fifth boom position 505.

[0038] Those of ordinary skill in the relevant art will understand that the method of boom control described above in accordance with FIGS. 5 and 6 is but one possible embodiment consistent with this disclosure. In other embodiments, other angles can be used for the respective ranges of motion without departing from the spirit and scope of the present invention. For example, in one such alternate embodiment, the fourth boom position 504 can be about 68 degrees, the fifth boom position 505 can be about 69 degrees, and the sixth boom position 506 can be about 70 degrees. Therefore, the invention should not be construed as limited to the particular embodiment illustrated in FIGS. 4 and 5. Instead, the invention should be construed to include all stability control methods and apparatuses that control stability of elevating systems, such as personnel lifts, by detecting angles of inclination relative to independent reference frames.

[0039] In accordance with the foregoing description, the stability control apparatus 210 described above with reference to FIGS. 2-5 can prevent the personnel lift 200 from being operated in an unstable manner by reducing the boom speed as the primary boom 201 approaches the top of its arc and, ultimately, by preventing the primary boom from pivoting beyond a predetermined angle. Although the foregoing embodiment represents one possible embodiment of the present invention, those of ordinary skill in the art will understand that other embodiments exist. For example, instead of controlling the rotational speed of the primary boom 201, an alternate embodiment of the stability control system 210 could instead control the rate of extension of the primary boom 201 along its longitudinal axis. In one aspect of this alternate embodiment, the various angles defining the different modes of operation of the primary boom 201 could vary depending on the amount of extension of the primary boom. For example, if the primary boom 201 was at full extension, then the limits of motion could be similar to those illustrated in FIG. 5. In contrast, if the primary boom 201 was less extended, then the ranges in motion could be somewhat broader than those shown in FIG. 5. These and other modifications can be made to the stability control apparatus 210 (FIGS. 2 and 3) in accordance with this disclosure.

[0040]FIG. 6 is an isometric view of a personnel lift 600 in accordance with an alternate embodiment of the invention. In one aspect of this embodiment, a primary boom 601 is pivotally connected to a secondary boom 602 at a first pivot point 671, and the secondary boom 602 is pivotally mounted to a turntable 620 at a second pivot point 672. The turntable 620 is rotatably mounted to a drive chassis 604. In a further aspect of this embodiment, a first angle detector 661 is operatively mounted to the personnel lift 600 proximate to the first pivot point 671 to detect the angle between the primary and secondary booms 601 and 602, and a second angle detector 662 is operatively mounted to the personnel lift proximate to the second pivot point 672 to detect the angle between the secondary boom 602 and the turntable 620. Similarly, a third angle detector 663 is mounted to the turntable 620 to detect the angle (positive or negative) between the turntable and an independent reference frame 641. In the illustrated embodiment of FIG. 6, the independent reference frame 641 is represented by a horizontal line normal to the direction of gravitational force. Accordingly, the independent reference frame 641 is independent from and unrelated to the position of the drive chassis 604.

[0041] In operation, the first, second and third angle detectors 661, 662 and 663 can be used to determine an angle of inclination 644 between the primary boom 601 and the independent reference frame 641. This angle of inclination 644 can then be used to control the stability of the personnel lift 600 using methods substantially similar to those described above in reference to FIGS. 4 and 5. For example, subtracting the angle between the secondary boom 602 and the drive chassis 604 from the angle between the primary boom 601 and the secondary boom 602 results in the angle between the primary boom 601 and the turntable 620. Once this angle is known, the angle between the turntable 620 and the independent reference frame 641 can be added or subtracted to it (as appropriate) to determine the angle of the primary boom 601 relative to the independent reference frame. As stated above, the angle between the primary boom 601 and the independent reference frame 641 can then be utilized as described above with reference to FIGS. 4 and 5 to control the stability of the personnel lift 600. As the foregoing example illustrates, various other angle detector configurations can be used to control the stability of a personnel lift in accordance with this disclosure. For example, as those of ordinary skill in the art will understand, the third angle detector 663 can be mounted to the chassis 604 and used substantially in accordance with the method described above to detect the angle between the primary boom 601 and the independent reference frame 641. Thus, for purposes of the discussion of FIG. 6, the turntable 620 may be considered to be part of the chassis 604, such that references to the “chassis” in this context would include both the chassis 604 and the turntable.

[0042] Although specific embodiments of, and examples for, the present invention are described here for illustrative purposes, various modifications can be made without departing from the spirit or scope of the present invention, as will be readily appreciated by those of ordinary skill in the relevant art. For example, the teachings provided here for a stability control apparatus can be applied not only to the personnel lift described above, but to other extendable systems where an instability may result from over extension or unfavorable chassis positioning. For example, the stability control apparatus disclosed here is equally suitable for use with personnel lifts not having extendable (e.g., telescoping) booms. Similarly, the stability control apparatus could also be used with extendable ladders for fire or rescue vehicles, in addition to elevators for transporting working materials to elevated locations.

[0043] These and other changes can be made to the invention in light of the above-detailed description. Therefore, the terms used in the following claims should be not construed to limit the invention to the specific embodiments enclosed, but in general should be construed to include all stability control apparatuses that operate in accordance with the claims. Accordingly, the invention is not limited by this disclosure, but instead its scope is to be determined entirely by the following claims. 

We claim:
 1. A stability control apparatus usable with a personnel lift, the personnel lift having a boom operatively connected to a chassis and a control system operatively connected to the boom for controlling movement of the boom relative to the chassis, the apparatus comprising: an angle detector adapted to be operatively mounted to the boom, the angle detector configured to detect an angle of inclination of the boom, the angle of inclination being an angle between a longitudinal axis of the boom and an independent reference frame independent of the chassis; and a signal processor operatively connected to the angle detector and adapted to be operatively connected to the control system, the signal processor configured to receive a first signal initiated by the angle detector when the angle of inclination reaches a predetermined angle, the signal processor further configured to output a second signal in response to receiving the first signal, the second signal causing the control system to limit movement of the boom relative to the independent reference frame when the angle of inclination reaches the predetermined angle.
 2. The stability control apparatus of claim 1 wherein the angle detector is configured to detect the angle of inclination between the longitudinal axis of the boom and a horizontal line at least substantially normal to the direction of gravitational force.
 3. The stability control apparatus of claim 1 wherein the angle detector is an accelerometer.
 4. The stability control apparatus of claim 1 wherein the angle detector is a pendulum switch.
 5. The stability control apparatus of claim 1 wherein the second signal causes the control system to limit pivotal movement of the boom relative to the independent reference frame when the angle of inclination reaches the predetermined angle.
 6. The stability control apparatus of claim 1 wherein the chassis is a drive chassis configured for repositioning of the personnel lift, wherein the control system is operatively connected to the drive chassis for controlling repositioning of the drive chassis, and wherein the second signal causes the control system to limit repositioning of the drive chassis when the angle of inclination reaches the predetermined angle.
 7. The stability control apparatus of claim 6 wherein the second signal causes the control system to prevent movement of the drive chassis from a first position to a second position when the angle of inclination reaches the predetermined angle.
 8. The stability control apparatus of claim 7 wherein the second signal causes the control system to prevent movement of the drive chassis from a first position having a first slope to a second position having a second slope greater than the first slope when the angle of inclination reaches the predetermined angle.
 9. The stability control apparatus of claim 1 further comprising an alarm system operatively connected to the signal processor, wherein the second signal causes the alarm system to activate when the angle of inclination reaches the predetermined angle.
 10. The stability control apparatus of claim 9 wherein the alarm system is a visual alarm system.
 11. The stability control apparatus of claim 10 wherein the visual alarm system includes flashing lights.
 12. The stability control apparatus of claim 9 wherein the alarm system is an audible alarm system.
 13. The stability control apparatus of claim 1 wherein the processor determines a boom speed based on the first signal received from the angle detector and outputs the second signal related to the boom speed.
 14. The stability control apparatus of claim 1 wherein the angle detector is configured to detect the angle of inclination between the longitudinal axis of the boom and a horizontal line at least substantially normal to the direction of gravitational force, and wherein the predetermined angle is between about 30 degrees and about 90 degrees.
 15. The stability control apparatus of claim 1 wherein the angle detector is configured to detect the angle of inclination between the longitudinal axis of the boom and a horizontal line at least substantially normal to the direction of gravitational force, and wherein the predetermined angle is between about 60 degrees and about 80 degrees.
 16. The stability control apparatus of claim 1 wherein the predetermined angle is a first predetermined angle, wherein the second signal causes the control system to reduce boom speed when the angle of inclination reaches the first predetermined angle, wherein the signal processor is further configured to receive a third signal initiated by the angle detector when the angle of inclination reaches a second predetermined angle, the signal processor further configured to output a fourth signal in response to receiving the third signal, the fourth signal causing the control system to stop movement of the boom relative to the independent reference frame when the angle of inclination reaches the second predetermined angle.
 17. A stability control apparatus usable with an elevating system, the elevating system having a boom operatively connected to a chassis and a control system operatively connected to the boom for controlling movement of the boom relative to the chassis, the apparatus comprising: an angle detector adapted to be operatively mounted to the elevating system, the angle detector configured to detect an angle of inclination, the angle of inclination being an angle between a portion of the elevating system and an independent reference frame independent of the chassis; and a signal processor operatively connected to the angle detector and adapted to be operatively connected to the control system, the signal processor configured to receive a first signal initiated by the angle detector and output a second signal in response to receiving the first signal, the second signal causing the control system to limit movement of the boom relative to the independent reference frame.
 18. The stability control apparatus of claim 17 wherein the angle detector is adapted to be operatively mounted to the boom and is configured to detect the angle of inclination between the boom and the independent reference frame.
 19. The stability control apparatus of claim 17 wherein the angle detector is adapted to be operatively mounted to the chassis and is configured to detect the angle of inclination between the chassis and the independent reference frame.
 20. The stability control apparatus of claim 17 wherein the angle detector is configured to detect the angle of inclination between a portion of the elevating system and a horizontal line at least substantially normal to the direction of gravitational force.
 21. The stability control apparatus of claim 17 wherein the second signal causes the control system to limit pivotal movement of the boom relative to the independent reference frame.
 22. The stability control apparatus of claim 17 wherein the chassis is a drive chassis configured for repositioning of the personnel lift, wherein the control system is operatively connected to the drive chassis for controlling repositioning of the drive chassis, and wherein the second signal causes the control system to limit repositioning of the drive chassis.
 23. The stability control apparatus of claim 22 wherein the second signal causes the control system to prevent movement of the drive chassis from a first position to a second position.
 24. The stability control apparatus of claim 23 wherein the second signal causes the control system to prevent movement of the drive chassis from a first position having a first slope to a second position having a second slope greater than the first slope.
 25. The stability control apparatus of claim 17 further comprising an alarm system operatively connected to the signal processor, wherein the second signal causes the alarm system to activate.
 26. The stability control apparatus of claim 17 wherein the processor determines a boom speed based on the first signal received from the angle detector and outputs the second signal related to the boom speed.
 27. A personnel lift comprising: a chassis; a boom pivotally connected relative to the chassis; a boom control system operatively connected to the boom for controlling movement of the boom relative to the chassis; an angle detector operatively mounted to the boom, the angle detector configured to detect an angle of inclination of the boom, the angle of inclination being an angle between a longitudinal axis of the boom and an independent reference frame independent of the chassis; and a signal processor operatively connected to the angle detector and the control system, the signal processor configured to receive a first signal initiated by the angle detector when the angle of inclination reaches a predetermined angle, the signal processor further configured to output a second signal in response to receiving the first signal, the second signal causing the control system to limit movement of the boom relative to the independent reference frame when the angle of inclination reaches the predetermined angle.
 28. The personnel lift of claim 27 wherein the boom is a primary boom having a first proximal end and a first distal end spaced apart from the first proximal end, and wherein the personnel lift further includes a secondary boom, the secondary boom having a second proximal end and a second distal end spaced apart from the second proximal end, the second proximal end of the secondary boom being pivotally connected adjacent to the chassis, and the first proximal end of the primary boom being pivotally connected to the second distal end of the secondary boom.
 29. The personnel lift of claim 27 wherein the boom is an extendable boom and the personnel lift further includes a lift cylinder operatively connected to the extendable boom and the boom control system for pivoting the boom relative to the chassis.
 30. The personnel lift of claim 27 wherein the angle detector is configured to detect the angle of inclination between the longitudinal axis of the boom and a horizontal line at least substantially normal to the direction of gravitational force.
 31. The personnel lift of claim 27 wherein the second signal causes the control system to limit pivotal movement of the boom relative to the independent reference frame when the angle of inclination reaches the predetermined angle.
 32. The personnel lift of claim 27 wherein the chassis is a drive chassis configured for repositioning of the personnel lift, wherein the control system is operatively connected to the drive chassis for controlling repositioning of the drive chassis, and wherein the second signal causes the control system to limit repositioning of the drive chassis when the angle of inclination reaches the predetermined angle.
 33. The personnel lift of claim 32 wherein the second signal causes the control system to prevent movement of the drive chassis from a first position having a first slope to a second position having a second slope greater than the first slope when the angle of inclination reaches the predetermined angle.
 34. The personnel lift of claim 27 further comprising an alarm system operatively connected to the signal processor, wherein the second signal causes the alarm system to activate when the angle of inclination reaches the predetermined angle.
 35. The personnel lift of claim 27 wherein the processor determines a boom speed based on the first signal received from the angle detector and outputs the second signal related to the boom speed.
 36. The personnel lift of claim 27 wherein the predetermined angle is a first predetermined angle, wherein the second signal causes the control system to reduce boom speed when the angle of inclination reaches the first predetermined angle, wherein the signal processor is further configured to receive a third signal initiated by the angle detector when the angle of inclination reaches a second predetermined angle, the signal processor further configured to output a fourth signal in response to receiving the third signal, the fourth signal causing the control system to stop movement of the boom relative to the independent reference frame when the angle of inclination reaches the second predetermined angle.
 37. The personnel lift of claim 27 wherein the boom is a primary boom having a first proximal end and a first distal end spaced apart from the first proximal end, and wherein the personnel lift further comprises: a base mounted to the chassis; and a secondary boom, the secondary boom having a second proximal end and a second distal end spaced apart from the second proximal end, the second proximal end of the secondary boom being pivotally connected to the base, and the first proximal end of the primary boom being pivotally connected to the second distal end of the secondary boom.
 38. The personnel lift of claim 27 wherein the boom is a primary boom having a first proximal end and a first distal end spaced apart from the first proximal end, and wherein the personnel lift further comprises: a rotatable base rotatably mounted to the chassis; and a secondary boom, the secondary boom having a second proximal end and a second distal end spaced apart from the second proximal end, the second proximal end of the secondary boom being pivotally connected to the base, and the first proximal end of the primary boom being pivotally connected to the second distal end of the secondary boom.
 39. An elevating system comprising: a chassis; a boom pivotally connected relative to the chassis; a control system operatively connected to the boom for controlling movement of the boom; an angle detector adapted to be operatively mounted to the elevating system, the angle detector configured to detect an angle of inclination, the angle of inclination being an angle between a portion of the elevating system and an independent reference frame independent of the chassis; and a signal processor operatively connected to the angle detector and adapted to be operatively connected to the control system, the signal processor configured to receive a first signal initiated by the angle detector and output a second signal in response to receiving the first signal, the second signal causing the control system to limit movement of the boom relative to the independent reference frame.
 40. The elevating system of claim 39 wherein the angle detector is adapted to be operatively mounted to the boom and is configured to detect the angle of inclination between the boom and the independent reference frame.
 41. The elevating system of claim 39 wherein the angle detector is adapted to be operatively mounted to the chassis and is configured to detect the angle of inclination between the chassis and the independent reference frame.
 42. The elevating system of claim 39 wherein the angle detector is configured to detect the angle of inclination between a portion of the elevating system and a horizontal line at least substantially normal to the direction of gravitational force.
 43. The elevating system of claim 39 wherein the second signal causes the control system to limit pivotal movement of the boom relative to the independent reference frame.
 44. The elevating system of claim 39 wherein the chassis is a drive chassis configured for repositioning of the personnel lift wherein the control system is operatively connected to the drive chassis for controlling repositioning of the drive chassis, and wherein the second signal causes the control system to limit repositioning of the drive chassis.
 45. The elevating system of claim 44 wherein the second signal causes the control system to prevent movement of the drive chassis from a first position to a second position.
 46. The elevating system of claim 44 wherein the second signal causes the control system to prevent movement of the drive chassis from a first position having a first slope to a second position having a second slope greater than the first slope.
 47. The elevating system of claim 39 further comprising an alarm system operatively connected to the signal processor, wherein the second signal causes the alarm system to activate.
 48. The elevating system of claim 39 wherein the processor determines a boom speed based on the first signal received from the angle detector and outputs the second signal related to the boom speed.
 49. A method for controlling the stability of a personnel lift, the personnel lift having a boom operatively connected to a chassis and a boom control system operatively connected to the boom for controlling movement of the boom relative to the chassis, the method comprising: providing an angle detector adapted to be operatively mounted to the boom, the angle detector configured to detect an angle of inclination of the boom, the angle of inclination being an angle between a longitudinal axis of the boom and an independent reference frame independent of the chassis; providing a signal processor operatively connected to the angle detector and adapted to be operatively connected to the control system, the signal processor configured to receive a first signal initiated by the angle detector when the angle of inclination reaches a predetermined angle, the signal processor further configured to output a second signal in response to receiving the first signal, the second signal causing the control system to limit movement of the boom relative to the independent reference frame when the angle of inclination reaches the predetermined angle; detecting when the boom has pivoted to the predetermined angle; and limiting movement of the boom when the boom has pivoted to the predetermined angle.
 50. The method of claim 49 wherein providing an angle detector includes providing an angle detector configured to detect the angle of inclination between the longitudinal axis of the boom and a horizontal line at least substantially normal to the direction of gravitational force.
 51. The method of claim 49 wherein providing an angle detector includes providing an accelerometer.
 52. The method of claim 49 wherein limiting movement of the boom when the boom has pivoted to the predetermined angle includes limiting pivotal movement of the boom relative to the independent reference frame.
 53. The method of claim 49 wherein limiting movement of the boom when the boom has pivoted to the predetermined angle includes limiting repositioning of the chassis.
 54. The method of claim 49 further comprising activating an alarm system when the boom has pivoted to the predetermined angle.
 55. The method of claim 49 further comprising determining a boom speed when the boom has pivoted to the predetermined angle.
 56. The method of claim 49 wherein limiting movement of the boom when the boom has pivoted to the predetermined angle includes limiting movement of the boom when the boom has pivoted to an angle between about 30 degrees and about 90 degrees.
 57. The method of claim 49 wherein limiting movement of the boom when the boom has pivoted to the predetermined angle includes limiting movement of the boom when the boom has pivoted to an angle between about 60 degrees and about 80 degrees.
 58. The method of claim 49 wherein limiting movement of the boom when the boom has pivoted to the predetermined angle includes reducing boom speed when the angle of inclination reaches a first predetermined angle, wherein providing the signal processor includes providing a signal processor further configured to receive a third signal initiated by the angle detector when the angle of inclination reaches a second predetermined angle, the signal processor further configured to output a fourth signal in response to receiving the third signal, the fourth signal causing the control system to further limit movement of the boom relative to the independent reference frame when the angle of inclination reaches the second predetermined angle, and wherein the method further comprises further limiting movement of the boom when the angle of inclination reaches the second predetermined angle.
 59. The method of claim 58 wherein further limiting movement of the boom when the angle of inclination reaches the second predetermined angle includes stopping boom movement.
 60. The method of claim 58 wherein further limiting movement of the boom when the angle of inclination reaches the second predetermined angle includes stopping chassis movement.
 61. A method of moving a boom from a first position to a second position, the boom being operatively connected to a chassis and a control system, the control system controlling movement of the boom relative to the chassis, the method comprising: detecting a boom angle relative to an independent reference frame independent of the chassis; allowing pivotal movement of the boom relative to the independent reference frame when the boom angle relative to the independent reference frame is within a first range; and limiting pivotal movement of the boom relative to the independent reference frame when the boom angle relative to the independent reference frame is within a second range, the second range including steeper angles of inclination than the first range.
 62. The method of claim 61 wherein limiting pivotal movement of the boom includes reducing boom speed relative to the independent reference frame.
 63. The method of claim 61 further comprising preventing pivotal movement of the boom when the boom angle relative to the independent reference frame is within a third range, the third range including steeper angles of inclination than the second range. 